1. Field of the Invention
The present invention relates to a honeycomb structure including a plurality of honeycomb segments joined integrally with a joining material layer. More specifically, the present invention relates to a honeycomb structure that effectively prevents generation of defects such as a crack caused of thermal stress that occurs in use and in regeneration of the honeycomb structure which is useful as an exhaust gas trapping filter, in particular, a diesel particulate filter (DPF) for trapping particulate matter (particulates) contained in the exhaust gas from a diesel engine.
2. Description of the Related Art
A honeycomb structure is incorporated in the exhaust system of a diesel engine or the like as a diesel particulate filter (DPF) as a filter to trap an exhaust gas for example in order to trap and remove particulate matter (particulates) contained in an exhaust gas from a diesel engine or the like. Such a honeycomb structure is prone to show uneven rise in temperature on the entire honeycomb structure when the honeycomb structure is in use (when trapping and removing particulates) and when the honeycomb structure is being regenerated (when burning and removing particulates deposited in a filter in order to remove the increase in the pressure loss caused by particulates chronologically deposited in the filter), thus being likely to cause defects such as a crack due to thermal stress. In order to eliminate such a disadvantage, a honeycomb structure has been proposed that reduces thermal stress through a constitution of a honeycomb segment joined body where a plurality of honeycomb segments comprising silicon carbide (SiC) with excellent heat resistance are joined integrally at respective joining surfaces via a joining material layer.
An SiC honeycomb structure is constituted by joining a plurality of honeycomb segments with a joining material as mentioned above. In case the adhesion of respective honeycomb segments is weak, longitudinal displacement (in the axis direction) or transverse displacement (normal to the axis direction) occurs in canning or in use (under vibration). To offset such a disadvantage, a honeycomb structure has been proposed that uses honeycomb segments whose flatness of the surface of its outer periphery is 0.2 mm or above (refer to JP-A-2001-138416).